Problem 72 - Objective Biology for NEET

Question

In amphibia, the heart has (a) Two auricles and two ventricles (b) Two auricles and one ventricle (c) One auricle and two ventricles (d) One auricle, one ventricle and one sinus venosus

Step-by-Step Solution

Answer

The correct answer is (b) Two auricles and one ventricle

Step 1: Elimination

First of all, it must be stated that the structure of amphibian hearts is quite distinct from that of higher organisms, such as mammals. For one, Amphibians do not possess two separate ventricles. This information helps us to eliminate options (a) and (c)

Step 2: Consideration

Now, we are left with options (b) and (d). Here, one needs to recall that an amphibia's heart does not consist of an extra component named 'sinus venosus', which leaves us with option (b) as the correct answer.

Key Concepts

Heart Chambers

Amphibians, such as frogs and salamanders, have a unique heart structure compared to mammals. Their heart consists of three chambers: two auricles (also known as atria) and one ventricle.

The atria are responsible for receiving blood. One atrium collects oxygen-poor blood from the body, while the other receives oxygen-rich blood from the lungs and skin.

Both types of blood are then pumped into a single ventricle.

• Two atria – handle separate streams of blood
• One ventricle – pumps both streams out

This structure allows for some mixing of oxygenated and deoxygenated blood in the ventricle, which is less efficient than the completely separated system in mammals. Nonetheless, it suits the needs of amphibians given their different metabolic and respiratory requirements.

Amphibian Physiology

Amphibians exhibit distinct physiological traits that align with their dual life habitats, both in water and on land. They have a permeable skin which allows them to absorb oxygen directly from water, supplementing their pulmonary respiration.

Their circulatory system is also adapted to support these habits. With a three-chambered heart, they can manage different oxygenation states of blood. This flexibility is crucial for amphibians as they transition between aquatic and terrestrial environments.

• Permeable skin – aids in respiration
• Three-chambered heart – supports flexible oxygenation
• Adaptations – support varying environments

This physiological adaptability reflects how amphibians are uniquely equipped to thrive in their niche habitats.

Sinus Venosus

The sinus venosus is a vital component in the hearts of some vertebrates, though it is not part of the adult amphibian heart. Instead, it has more significance in the early developmental stages. In other vertebrates, nnotably fish and some reptiles, it functions as a chamber where blood collects before entering the atrium.

However, in the case of adult amphibians, particularly frogs, the sinus venosus becomes less prominent and sometimes may not be individually distinct from the rest of the heart.

• Early development – present in young stages
• Reduced role in adults – not a separate chamber
• Connects with the atrium – role in blood collection

Understanding the sinus venosus helps provide insights into the evolutionary progression and physiology of different vertebrates.